Rollup merge of #95298 - jhorstmann:fix-double-drop-of-allocator-in-vec-into-iter...

Rollup merge of #95298 - jhorstmann:fix-double-drop-of-allocator-in-vec-into-iter, r=oli-obk

Fix double drop of allocator in IntoIter impl of Vec

Fixes #95269

The `drop` impl of `IntoIter` reconstructs a `RawVec` from `buf`, `cap` and `alloc`, when that `RawVec` is dropped it also drops the allocator. To avoid dropping the allocator twice we wrap it in `ManuallyDrop` in the `InttoIter` struct.

Note this is my first contribution to the standard library, so I might be missing some details or a better way to solve this.